The invention provides a hydraulic 
chassis engineering machine step control method, which includes testing the 
current load state of the 
engineering machine, the opening degree of the 
throttle, and the actual run speed. The invention judges the 
current load state, when the load state is intermediate low, and the difference of the actual speed and the goal rotate speed exceeds the preset range, then corresponding current can be provided for the 
hydraulic motor for regulating the displacement; namely when the actual rotate speed is lower than the goal rotate speed, current for lowering the displacement can be provided to the 
hydraulic motor; when the actual rotate speed is higher than the goal rotate speed, the current for improving the displacement can be provided to the 
hydraulic motor; when the load state is in overload, the displacement of the hydraulic motor can be adjusted to the maximum. The required power of the 
system can be calculated according to the current displacement of the hydraulic motor, the demand of the rotate speed, and the current pressure of the 
system. Current, the displacement of which can meet the requirement of the controller, is provided for the 
hydraulic pump according to the required power of the 
system, and the needed displacement can ensure that the power absorbed by the 
hydraulic pump can meet the requirement of the hydraulic motor. Compared with the prior art, the invention can enable the 
engineering machine to realize the control requirement accurately.